Fuel cell crimp-resistant cooling device with internal coil

ABSTRACT

A cooling assembly for fuel cells having a simplified construction whereby coolant is efficiently circulated through a conduit arranged in serpentine fashion in a channel within a member of such assembly. The channel is adapted to cradle a flexible, chemically inert, conformable conduit capable of manipulation into a variety of cooling patterns without crimping or otherwise restricting of coolant flow. The conduit, when assembled with the member, conforms into intimate contact with the member for good thermal conductivity. The conduit is non-corrodible and can be constructed as a single, manifold-free, continuous coolant passage means having only one inlet and one outlet. The conduit has an internal coil means which enables it to be bent in small radii without crimping.

The Government has rights in this invention pursuant to Contract No.NASA DEN 3-241.

BACKGROUND OF THE INVENTION

This invention relates to an improved cooling apparatus, and, morespecifically, to an improved cooling assembly for use in fuel cellstacks.

Cross-reference is made to two other copending patent applicationspertaining to related subject matter and assigned to the same assigneeas this application; application of Arthur Kaufman and John Werthentitled "Cooling Assembly For Fuel Cells", Ser. No. 06/500,498, filedon June 2, 1983; and application of John Werth entitled "Fuel CellCrimp-Resistant Coolant Device With Internal Support", Ser. No. 740,303filed June 3, 1985, continuation of Ser. No. 06/500,464, filed on June2, 1983 now abandoned. These applications are incorporated by referencein their entireties herein.

Fuel cell design and operation typically involves conversion of ahydrogen-containing fuel and some oxidant into DC electric power throughan exothermic reaction. The chemistry of this reaction is well known andhas established parameters and limitations. One such limitation is thatthe electrochemcial reaction produces, as a by-product thereof,substantial waste heat which must be removed in a controlled manner tomaintain the cells at their desired operating temperature. For efficientoperation, it is generally desirable to maintain the cells atsubstantially uniform temperature and at a temperature level which isconsistent with a cntrollable rate of reaction of the fuel cellstherein.

Conventional methods for removal of waste heat from the fuel cellenvironment have traditionally involved the use of a laminar heatexchanger assemblies, or cooling assemblies, incorporated within andarranged parallel to the various other layers from which the fuel cellsare constructed. Typically, the components of the cooling assembly takethe form of passageways which contain a circulating coolant material.The heat generated within the stack is transferred to the coolant as itis circulated through the stack. The coolant is then brought out of thestack and into a heat exchanger where the heat is removed therefrombefore the coolant is recirculated through the stack. In this manner thecooling assembly enables control over the temperature of the reactionenvironment of the fuel cell stack and, thus, its rate and efficiency.The pattern of distribution of the coolant passageways within the stack,their relative size, the heat capacity of the coolant fluid and thevolume of coolant which is circulated through the cooling assembly perunit of time determine the heat transfer capacity of the cooling system.Because the cooling system is generally an integral part of the fuelcell stack, it should be electrically isolated from the stack and alsoshould not be adversely affected by corrosive media within the stacksuch as the hot electrolyte.

The problems associated with corrosion as well as the undesirable flowof electrical current from the stack into the cooling loop are describedin detail in U.S. Pat. Nos. 3,964,929; 3,964,930; and 3,969,145. Thesepatents address the problem of the so-called "shunt currents" andattempt to resolve it by electrically insulating the cooling system fromground. This minimizes the driving potential of such currents relativeto the coolant. Other techniques for avoiding the problems associatedwith shunt currents include the use of dielectric coolants.

The heat exchanger configuration described in these patents is rathertypical of that employed by the prior art. Generally, the configurationconsists of a series of parallel tubes connected to what is generallyreferred to as a "plenum". The plenum is a reservoir from which coolantis simultaneously distributed into the parallel tubes which are embeddedin a fuel cell cooling assembly. After passage of the coolant throughthe parallel tubes, it is collected in another plenum and, thereafter,returned, through a cooling loop, to the inlet plenum.

The cooling assembly tubes are composed of electrically conductivematerial such as copper. Water can be used as the coolant and the metaltubes are coated either on their internal or external surfaces with adielectric material such as polytetrafluoroethylene. This coating isused to reduce the possibility of shunt currents and corrosion of thetubes. The coated tubes are located in passageways formed in the platesof fuel cells in the stack. However, due to manufacturing tolerances, itis difficult to avoid voids such as spaces between the tubes and thewalls of the passageways. Since air is a poor conductor of heat, suchair spaces can be filled with a thermally-conductive grease which iscompatible with the electrolyte to maximize heat transfer from the cellsto the coolant. These systems also use a sacrificial anode material atthe tube ends to guard against corrosion. In addition, there is thepossibility of discontinuities occurring in the Teflon layer such as bymanufacturing imperfections, differential thermal expansion, damageduring the assembly process, poor bonding, etc. This causes twoproblems; first the corrosive media in the fuel cell will be able todirectly attack the tube and second, the thermal contact will bediminished.

A variation in cooling assembly design is disclosed in U.S. Pat. No.4,233,369. In this patent, a fibrous, porous coolant tube holder, whichalso serves as a member through which a reactant gas can travel, is usedto hold copper coolant tubes. The tubes, held in channels in the holder,are connected to a coolant inlet header and coolant outlet header.Between the headers, the tubes pass through the stack, make a U-turn andpass back through the stack. The tubes are pressed into the channels andhave caulking between the channel walls and tube. In addition to reducedcorrosion, this system makes the separator plate thinner and easier tomanufacture.

Other techniques are known for bringing coolant materials into a fuelcell stack. For instance, a tubeless system has been used wherein ametal plate is grooved in a pattern on its surface with one or moreinlets and outlets. The grooved surface of the plate is then coveredwith a second ungrooved metal plate, called a brazing sheet, to createan assembly having enclosed coolant passageways and coolant inlet andoutlets. In addition, similar passageways can be constructed byassembling two such brazing plates with partitions therebetween whichform coolant passageways.

It is evident that the demands upon the cooling systems for fuel cellsare significantly greater and more specialized than those encountered byother devices in different heat transfer environments. U.S. Pat. Nos.1,913,573; 2,819,731; 2,820,615; 2,864,591; and 3,847,194 areillustrative of some of the conventional heat transfer devices found inareas other than the fuel cell-related technologies. In virtually allthe heat exchangers described in the immediately foregoing list ofpatents, the environmental setting contemplated for their use is muchmore forgiving than that encountered in fuel cells.

Accordingly, it is a principal object of the invention to provide animproved fuel cell cooling assembly.

It is another object of the invention to provide a cooling assembly thatmaximizes heat transfer from the fuel cell stack to the coolant withoutundue manufacturing and assembly tolerances.

It is another object of this invention to provide a manifold-freecooling assembly of simplified construction.

It is another object of the invention to provide a cooling assemblywhich is essentially non-corrosive in the fuel cell environment.

It is another object of this invention to provide a cooling assemblywhich avoids shunt currents without the need for additional electricalisolation thereof from adjacent fuel cells within the stack.

It is another object of this invention to provide a cooling assemblythat can be an integral component of a fuel cell.

It is another object of the invention to provide a cooling assembly thatavoids coatings.

SUMMARY OF THE INVENTION

The fuel cell cooling assembly described herein utilizes a conformableconduit for carrying coolant through the assembly. The conduit is heldby a member or members containing channels which, upon assembly with theconduit, conform the conduit into intimate contact with the surface orthe channels to maximize heat transfer from the fuel cell to thecoolant. The conduit may comprise a non-corroding, metal, free,dielectric material. The conduit may be a continuous tube havinginternal coil means therein to accommodate the bends necessary toarrange the conduit into a serpentine configuration without crimping.The conduit maximizes a heat transfer in a given area whilenecessitating only one inlet and one outlet for the coolant.

In another embodiment, the cooling assembly can be used in a stack ofdiscrete fuel cells in which two of the discrete adjacent cells areseparated from one another by a manifold-free heat exchanger assemblycomprising a termination plate from each of the adjacent cells which, incombination, form a predetermined channel pattern to intimately cradle acontinuous, non-corrodible, crimp-resistant, electrically insulatedconduit.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will now be described by reference to the followingdrawings and description in which like elements have been given commonreference numerals:

FIG. 1 is a schematic representation of a fuel cell assembly comprisinga plurality of stacked fuel cells with intermediate cooling plates andterminal current collecting plates.

FIG. 2 is a perspective view of a portion of the fuel cell assembly ofFIG. 1, illustrating an individual fuel cell in greater detail.

FIGS. 3(a) and 3(b) are a perspective view showing two embodiments ofthe cooling assembly.

FIG. 4(a) is a view in partial cross section of a cooling assembly whichhas been isolated from the fuel cell assembly illustrating theserpentine arrangement of conduit means as it weaves through thepredetermined channel pattern formed in the members which retain theconduit means.

FIG. 4(b) is a top view of FIG. 4(a).

FIG. 5 is a cross section through FIG. 4(a) at Section A--A.

FIGS. 6(a) and 6(b) are views of the intimate contact between theconduit means and members of the cooling assembly.

FIGS. 7(a) and 7(b) are schematic illustrations of the formation of thetruncated half circle grooves.

FIGS. 8 a-c are schematic illustrations of the coolant tube and thegrooves at various times.

FIG. 9 is a schematic illustration of the coil pattern after the coilmaterial is stretched out between those sections thereof to accommodatebends in the coolant tube.

FIG. 10 is a schematic illustration of the coil support in the coolanttube before the tube is bent, the tube being partially cut away.

FIG. 11 is a schematic illustration of the coil support in a tubearranged in serpentine configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An exemplary fuel cell stack assembly 10 employing the invention isshown in FIGS. 1 and 2. The stack assembly 10 includes a plurality offuel cells 11. Hydrogen gas input manifolds 12 are arranged along oneside of the stack assembly 10. Although a plurality of manifolds 12 areshown for each group of fuel cells 11, a single such manifoldarrangement could be used if desired. The manifolds 12 are connected toa source of hydrogen gas 14. Hydrogen gas collecting manifolds 15 arearranged along the opposing stack side in correspondence with thehydrogen gas input manifolds 12. Here again, although a plurality ofmanifolds 15 are shown, a single such manifold could be used if desired.The collecting manifolds 15 are connected to a hydrogen gas dischargingor recirculating system 17. The hydrogen gas from the input manifolds 12flows through gas distribution plates 18 to the collecting manifolds 15.

In similar fashion, a plurality of oxygen input manifolds (not shown)are arranged along another stack side connecting the one stack side andthe opposing stack side. These oxygen manifolds are connected to anoxygen source 19. The oxygen may be supplied in the form of air ratherthan pure oxygen if desired. A plurality of oxygen collecting manifolds(not shown) are arranged along the stack side opposing the stack sidehaving the oxygen input manifolds connecting the respective one stackside and opposing stack side. The stack sides at which the oxygenmanifolds are arranged are generally stack sides other than the ones atwhich the hydrogen input manifold and hydrogen collecting manifold areconnected. The oxygen manifolds are also connected to an oxygen storageor recirculating system (not shown). The oxygen from the input manifoldsflows through the oxygen gas distribution plates 20 to the respectivecollecting manifolds.

Cooling assemblies 21 are arranged periodically between adjacent fuelcells 11 to effect the desired degree of cooling. In the embodimentshown in FIG. 1, three cooling assemblies 21 are shown arrangedintermediate each group of four cells 11. The cooling material, eitherliquid or gas, which flows through the cooling assembly 21 can be anysuitable material. For instance, it can be a dielectric fluid such as ahigh temperature oil coolant manufactured by Multitherm Corporationunder the trade name PG-1. In the alternative, it can be anon-dielectric coolant such as water or water & stream mixtures.

A pump 22 circulates the coolant by way of passageway 23 anddistribution reserovir 24 into the respective cooling assemblies 21. Thedistribution reserovir 24 is joined to each individual cooling assemblyby direct connection to the inlet port of the continuous coolant conduit90 of cooling assembly 21. Conduit 90 is shown in two differentconfigurations in FIGS. 3(a) and 3(b). After passing through conduit 90,the coolant flows into the collection reservoir 25. The reservoir 25 isconnected to a heat exchanger 26 which reduces the temperature of thecoolant to the desired input temperature before it is recirculatedthrough the conduit 90. Collection reservoir 25 is joined to the coolingplate assemblies 21 by direct connection to the outlet port ofcontinuous conduit 90. A coolant passageway 27 connects the heatexchanger 26 back to the pump 22 so that the coolant can be recirculatedthrough the respective cooling assemblies 21.

Reservoirs 24 and 25, referred to hereinabove, are ordinarily onlypresent when the fuel cell stack 10 has a number of cooling assemblies21, and even then the reservoirs are connected directly to eachindividual cooling assembly 21 at a single point. Alternatively,however, cooling assembly designs could be made wherein more than onecontinuous conduit 90 operates in parallel to effect serial distributionof coolant throughout the plate or wherein such multiple continuousconduits are complementary to one another and each independentlydistributes coolant throughout the plate.

The fuel cells 11 and the cooling assemblies 21 are basicallyelectrically conductive so that when they are stacked as shown, the fuelcells 11 are connected in series. In order to connect the stack assembly10 to a desired electrical load, current collecting plates 28 areemployed at the respective ends of the stack assembly 10. Positiveterminal 29 and negative terminal 30 are connected to the currentcollecting plates 28 as shown and may be connected to the desiredelectrical load by any conventional means.

Any suitable fuel cell design can be utilized with the cooling assemblydisclosed herein. FIG. 2 depicts a cooling assembly 21 together withportions of a representative fuel cell stack shown in more detail. Thisfigure includes two portions of the stack immediately surroundingcooling assembly 21. Each of the stack portions includes in thisembodiment, a plurality of fuel cell units 11. The stack portion to theright of the cooling assembly 21 (in solid lines) shows detail of thevarious components of the cell 11. The stack portion to the left ofcooling assembly 21 (in dotted lines) is representative of anothersimilar fuel cell. Although the portion of the stack in dotted lines isshown slightly removed from the portion in solid lines for clarity, itis understood that these two portions are in contact with each other andconduit 90 in actual operation to provide good electrical and thermalconductivity through the two portions.

Each fuel cell 11, as depicted in FIG. 2 includes a hydrogen gasdistribution plate 18 and an oxygen or air distribution plate 20.Arranged intermediate between the respective gas distribution plates 18and 20 are the following elements starting from the hydrogen gasdistribution plate 18; anode 31, anode catalyst 32, electrolyte 33,cathode catalyst 34 and cathode 35. These elements 31-35 of the fuelcell 11 may be formed of any suitable material in accordance withconventional practice.

The hydrogen gas distribution plate 18 is arranged in contact with theanode 31. Typically, the anode comprises a carbon material having poreswhich allow the hydrogen fuel gas to pass through the anode to the anodecatalyst 32. The anode 31 is preferably treated with Teflon(polytetrafluoroethylene) to prevent the electrolyte 33, which ispreferably an immobilized acid, from flooding back into the area of theanode. If flooding were allowed to occur, the electrolyte would plug upthe pores in the anode 31 and lessen the flow of hydrogen fuel throughthe fuel cell 11. The anode catalyst 32 is preferably a platinumcontaining catalyst.

The fuel cell 11 is formed of an electrically conductive material, suchas a carbon based material, except for the electrolyte layer which doesnot conduct electrons but does conduct hydrogen ions. The variouselements, 18, 31-35, and 20 are compressed together under a positivepressure during the cell assembly process. The electrolyte 33 can bemade of any suitable material such as phosphoric acid. The acid can bedispersed in a gel or paste matrix so that it is immobilized and not afree liquid. An exemplary electrolyte matrix could comprise a mixture ofphosphoric acid, silicon carbide particles and Teflon particles. Thecathode catalyst 34 and the cathode 35 can be formed of materialssimilar to the anode catalyst 32 and anode 31.

All of the elements of the fuel cell 11 are arranged after assembly inintimate contact as shown in FIG. 2. In order to provide a relativelycompact electrically interconnected stack assembly of a plurality ofadjacent individual fuel cells 11, the bi-polar assembly 36 is used toeasily connect together adjacent fuel cells 11. The bi-polar assembly 36is comprised of a hydrogen gas distribution plate 18 and an oxygen orair distribution plate 20 with the impervious interface layer of plate37 arranged between them. Therefore, the bi-polar assembly 36 iscomprised of the hydrogen gas distribution plate 18 of one cell 11 andthe oxygen or air gas distribution plate 20 of the next adjacent cell11. The interface layer, or plate 37, may comprise an impervious carbonplate or any other conventional interface as may be desired. Thebi-polar assembly 36, the plates 18 and 20 and the interface 37therebetween are securely connected together as a unit so as to havegood electrical conductivity.

In order to facilitate the gas flow in the gas distribution plates 18and 20, respective channels or grooves 38 or 39 are employed. Thegrooves 38 in the hydrogen gas distribution plate 18 are arrangedorthogonally or perpendicularly to the grooves 39 in the oxygen or airgas distribution plate 20. This allows the grooves to be easilyconnected to respective input and output manifolds 12 and 15, forexample, on opposing sides of the cell stack assembly 10. Althoughgrooves within a particular plate, such as plates 18 or 19, are shown asextending in a unidirectional manner in FIG. 2, there can becross-channels made between these grooves to aid in the distribution ofthe fluidic reactants. When such cross-channels are utilized, theprimary flow of reactants is still in the direction of the grooves 38and 39 as shown in FIG. 2; that is, in the direction that the reactantsflow between the reactant input and collecting manifolds.

The gas distribution plates 18 and 20 supply the respective hydrogen andoxygen or air gases to the surfaces of their respective anode 31 orcathode 35. In order to more evenly distribute the respective gases atthe anode 31 or cathode 35 plate surfaces, the gas distribution plates18 and 20 are preferably formed of a porous carbon material. This allowsthe gases to flow through the pores of the plates 18 and 20 between thechannels 38 or 39 to provide more uniform gas distribution over the faceof the respective anode 31 or cathode 35.

At the ends of the stack, as seen in FIG. 1, there are currentcollecting plates 28. These can be made an integral part of the adjacentgas distribution plate assembly on the end cell in the stack.Optionally, an impervious material, such as aluminum, can be placedbetween the gas distribution plate and current collecting plate or thecurrent collecting plate itself can be made of such a material.

The cooling assembly 21, as shown in FIG. 2 and also FIGS. 4(a) and 4(b)has at least one coolant conduit means such as conformable tube 90. Theconduit carries coolant through the cooling assembly 21. The coolingassemblies 21 shown in FIGS. 3-5 include a means for holding the conduittube 90 in the assemblies including a member or plate 41. The member 41,when assembled with the conduit tube, conforms at least a portion of theconduit tube into intimate contact with the member 41.

The embodiment of the cooling assembly 21 shown in FIG. 2 includes themember 41 as an integral part of the gas distribution assembly 40. Theassembly 40 includes hydrogen gas distribution plate 18 and a gasimpervious plate 42, which is optional, assembled together with themember 41. A similar assembly is shown in dotted lines on the left sideof tube 90, except that the oxygen gas distribution plate 20 is made anintegral part of the assembly. The gas distribution plates 18 and 20could alternatively be film bonded directly onto member 41.

The improved cooling assembly 21 can take several embodiments, two ofwhich are shown in more detail in FIGS. 3(a) and 3(b). In a firstembodiment shown in FIG. 3(a), conduit 90 is a single, continuous tubehaving one inlet and one outlet for coolant. The tube is arranged in aserpentine or similar pattern within members 41 to effect good heattransfer between the members 41 and the tube 90. Although the tube 90 isshown as having its turning bends outside members 41 to sweep back andforth across members 41, the turning bends can alternatively be placedwithin the members 41. In a second embodiment shown in FIG. 3(b),conduit 90 is actually a pluality of conduit tubes 90 passing throughthe members 41. Coolant, in this latter embodiment, is brought in andexited through a manifold comprising conduit feeders or headers 90' sothat all conduits 90 can be fed off a single conduit feeder.

The embodiment shown in FIG. 3(a) is the preferred one. This is themanifold-free arrangement which is simpler and less expensive tomanufacture and assemble as compared to the arrangement shown in FIG.3(b). The phrase "manifold-free" is intended as descriptive of a heatexchanger in which a coolant is distributed from the portion of thecooling loop which is remote from the fuel cells directly into thecooling assembly so as to provide for serial flow of coolant throughoutthe cooling assembly. This is in sharp contrast to the devicesillustrated in the prior art whereby coolant is simultaneouslydistributed from a common manifold into a plurality of parallel, andhighly localized, channels of the cooling plate which is served by eachof these individual unconnected coolant paths.

As can be readily appreciated, the phrase "manifold-free" is not,however, intended as exclusive of a coolant distribution system whereincoolant from a common source is simultaneously distributed into two ormore continuous channels or conduits arranged in parallel, or otherwise,within the cooling assembly. The coolant flow in this latter type systemwould not be of the highly localized nature as in the prior art, butrather would and could provide (a) a redundant coolant flow pattern, (b)two or more patterns which are complementary to one another, or (c) acoolant flow pattern in which the direction of flow in one channel iscountercurrent to the flow in the other. In any event, thispredetermined pattern of distribution of a second continuouschannel/conduit would not be highly localized as is dictated by theprior art systems in which a manifold is an essential element for thesimultaneous distribution of coolant through such unconnected localizedchannels.

In the event a corrosion sensitive material is used in the fabricationof this cooling assembly, it should be effectively isolated from theelectrolyte and other hostile chemical agents. In the most preferredembodiments of this invention, the cooling assembly is essentiallymetal-free; that is, none of the components thereof which are actuallyor potentially exposed to the corrosive environment of the fuel cell arecomposed of a corrosive material such as metal. For example, conduit 90is preferably a fluorinated hydrocarbon polymer. In fuel cells, the gasdistribution plates, such as 18 and 20 in FIG. 2, are commonly made of aporous carbon material. To protect the members 41 from corrosion, animproved interfacial layer configuration can be used between members 41and gas distribution plates 18 and 20 to replace gas impervious plate42. This interfacial configuration is described in the copending U.S.patent application Ser. No. 06/430,148, filed on Sept. 30, 1982 entitled"Film-Bonded Fuel Cell Interface Configuration", invented by A. Kaufmanand P. L. Terry, which is incorporated herein by reference in itsentirety.

FIGS. 4(a), 4(b) and 5 show further views of the cooling assembly 21. Inthis embodiment, the cooling assembly 21 consists of conformable coolantconducting means, the tube 90, for carrying coolant through the coolingassembly. Coolant is brought in through one end of the tube 90, theinlet 45, and removed from the assembly at the other end of tube 90, theoutlet 46. A means similar to that described in FIG. 1 is used tocirculate the coolant through the cooling assembly. The coolant assemblyis located adjacent a cell or between two adjacent cells in a fuel cellstack as shown in FIG. 1. The cooling apparatus includes a means forholding the tube 90, in this embodiment shown as members 41. The member41 has means therein for holding the tube 90 such as channels 43 shownin FIG. 5. When the members 41 are assembled together with the tube 90,at least a portion of the tube 90, and particularly the surface area ofthe tube, conforms to make intimate contact with the member 41.

The conduit means, the tube 90, is preferably non-corrodible andmetal-free. The tube 90 can be made of any suitable material such as adielectric material. One material suitable for this purpose ispolytetrafluoroethylene (Teflon). Thus, tube 90 can be a Teflon tubehaving about a 0.270 inch outside diameter and a 0.015 inch wallthickness. It also is preferably a single, continuous length of tubehaving one inlet and one outlet to eliminate complex inlet and outletmanifolds. It can be placed in a zig-zag or serpentine configurationwith periodic bends therein to sweep it back and forth across thecooling member 41. The bends in tube 90 may occur outside the member 41,as shown in FIG. 4, or, alternatively, may occur within the member.

In the use of a Teflon tube in cooling assemblies, some considerationshould be given to the pressure limits of the tube. A tube such as thetype described immediately above was operated in a fuel cell having anormal operating temperature of about 350°-400° F. It was found that thespecific tube used might burst if coolant pressures were maintained inthe area of 100 psi and above. On the other hand, bursting did not occurwhen the pressure was maintained in a range up to approximately 50-60psi.

The areas of the tube 90 which are bent can be made to bend as desiredby any suitable means. For instance, the tube 90 can be manufactured tohave predetermined bends in it such as approximately 180° beforeassembly with member 41. Its shape can conform to the serpentinearrangement it should follow to pass through channels 43 when thecooling assembly is put together. The tube 90 can also be made of astraight section of tubing which is bent into the serpentine arrangementduring assembly with members 41. To ease the bending process, corrugatedsegments can be periodically arranged along its length to allow forshort radius bending thereof without crimping or other damage or failureoccurring to the tube as it is arranged within the predetermined channelpattern formed by members 41.

The corrugations are typically less than one or two inches in length andthey permit a tight bending radius to allow a tightly-packed, zig-zaggeometry that yields a high ratio of heat transfer area to total platearea. The bends can be 180° or some other angle to accommodate thepattern of sweeping the tube back and forth across members 41. Onemethod of creating such corrugations is to apply a hot mandrel to thosesections of the tube where the tube is to be bent. The tube material,such as Teflon, is thereby softened by the hot mandrel while also beingconstrained by the mandrel. The tube wall in this condition takes on afluted (or corrugated) configuration.

Instead of corrugating tube 90 in its portions which are to be bent,other approaches can be used in bending the tube 90 to allow short radiiwithout the risk of crimping the tube or causing other damage to it. Onesuch approach is to provide a support means in the tube to guard againstsuch damage. The internal support can be placed throughout the length ofthe tube or only at the locations at which the tube is to be bent. Sucha support can be located entirely within the tube's central passagewaythat carries the coolant, and it can be an additional componentassembled to the tube.

A preferred type of internal support means is carried out by insertingwire coils inside the tube at the locations that the tube is to be bent.This is shown in FIGS. 9-11. Such coil 70 can have a diameter slightlyless than the inside diameter of the tube 90 and enable the coolant topass through inside diameter of the coil as well as around the coils andbetween the coils and tube wall. Coils have been found to prevent excesscrimping in the tube wall when the tube is formed into short radiusbends 72. The coils at the bends can be connected to one another by anysuitable means such as by a straight section 74 of wire therebetween.The coils can be inserted into the tubing by their leading end and fullypushed into the entire length of the tube. In this manner, thetightly-wrapped coil portions 70 are located in the area 72 of the tubeto be bent while the straight sections 74 are located along the tubebetween the bends.

The coils can be made of any suitable material. For instance, they canbe safely made of a metallic material such as steel since they arecompletely located in the tube and, thus, are not exposed to thecorrosive materials used in the fuel cell environment. The approach ofusing an internal support such as a coil in the tube is believedsignificantly less expensive to manufacture than the placement ofcorrogations in the tube material itself as described above. The shape,size and configuration of the internal support can be any suitable oneso long as the coolant is allowed to flow in the tube as intended.

One manner of forming the metal coil internal support is to start with alength of tightly-wrapped coil or spring stock of an appropriate lengthand diameter and stretch out the coil material in conformance with thefrequency of bends in the tube. A small, still tightly-wrapped length 70can be left between each uncoiled section 74 sufficient to accommodate abend in the tube. The portion of the coil support structure between thebends is then simply a straight uncoiled section of coil material joinedto tightly-wrapped sections of coil at the bends. In this manner, theentire internal support can be made of a single continuous length ofcoil material.

The coil pattern; e.g., tightly-wrapped coil sections separated byuncoiled sections, could be manufactured by hand with suitable coilstretching and anchoring tools to match the intended configuration ofthe bends of the tube in the cooling assembly. To provide a coil patternof greater dimensional control and accuracy, any conveniently availablemechanism can be used. For instance, an ordinary lathe was used toprocess a length of tightly-wrapped coiled material into a coil patternwith sections of tightly-wrapped coil interspersed with uncoiled,stretched out lengths of coil material. The lathe was used simply as aholding and stretching device and not in its usual machining capacity.

The coil was placed in the chuck of the lathe with a section extendingout towards the tools carriage along the lathe bed. A clamp or someother appropriate forcing device was attached to the extending sectionof the coil, but leaving a tightly coiled portion beyond. The clamp wasthen moved away from the chuck to stretch out the coil into a somewhatstraight section so as to deform the coil material in that area. Thisprovided a tightly-wrapped coil section separated from the rest of thecoil by a relatively unwrapped or straight section of coil material. Thecoil stock was then loosened in the chuck and moved a bit to allowanother tightly-wrapped coil section thereof to extend beyond the chuck.The clamp was then again fastened on the coil stock having atightly-wrapped portion between it and the previously stretched outportion to be placed in a bend in the tube. After this section wasstretched, the process was repeated until there were enoughtightly-wrapped coiled sections of coil material between stretched outsections to accommodate all the bends in the tube.

The coil pattern manufactured in this manner was used in a coolingassembly with good results. There was enough space within the innerdiameter of the coil so as not to unduly impede the flow of coolant. Forinstance, a tube having a nominal size of 1/4 inch diameter was used,the inside diameter thereof being approximately 0.270 inches. A coilhaving an outside diameter slightly less than the inside diameter of thetube and inside diameter of approximately 0.190-0.200 inches, made inthe above-described manner, was screwed into a length of tubeapproximately 30 feet long. In using the tube with the coil insertedtherein the pressure drop across the entire tube length was held to lessthan 20 psi.

In addition to the coil-type internal support, other types of internalsupports can be used. For instance, an internal cylindrical or tube ormember of other configuration could be placed in the coolant tube toease crimping in the bend areas. Such an internal tube should be rigidso as not to overlay restrict or impede coolant flow yet enable smallradius bends in the coolant tube. Internal tubes for this purpose can bemade out of any suitable material such as plastic or metal.

The channels 43 within members 41 can take any pattern which is suitablefor cooling. The contour of the channels 43 may preferably have theshape that approximately conforms with the natural peripheral shape oftubes 90. This is so that when members 41 are placed over the tubes 90,there is an intimate surface-to-surface contact between the twocomponents and a minimization of any air spaces or other voidstherebetween. Any such gaps that might otherwise exist are closed by thetube conforming to the surface contour of the channels 43. The sizing ofthe channels 43 relative to the sizing of the tubes 90 may be such thatthe channel at least slightly compresses the tube periphery when the twoare assembled into operating positions. Thus, the channel 43 takes on ashape which closely conforms to the tube 90 when the two are assembledtogether.

The cooling assembly 21 can be made as a separate unit from theindividual cells of the fuel cell stack so that members 41 and conduitmeans 90 can be placed or inserted periodically along the stack topermit cooling. Alternatively, members 41 can be made part of orintegral with the gas distribution plates of the fuel cell adjacent tothe cooling assembly. In this configuration, two such stack portionshaving an integral member 41 on the end cell can be assembled with thecooling tubes to form a cooling assembly within the stack.

The function of the straight sections of tube 90 is to effect thetransfer of heat from the grooved surfaces 43 in members 41 in whichthey are nestled. The members 41, containing the grooved surfaces, canbe made of any solid, thermally and electrically conductive material,such as any material commonly used in hot fuel cell or battery plates.

The grooves or channels 43 in member 41 can assume any suitablecross-section profile to accomplish the result desired. The channelshape can be formed to conform the tube 90 to its shape and therebycause intimate contact therewith when assembled. For instance, thegrooves in each member 41 can be cut in an approximately half-round orhalf-oval cross-section. The surfaces of the members 41 can then bemechanically pressed together with the grooves over the tube 90. Thesurfaces of the members between the grooves can be brought into contact,as shown in FIGS. 5-6, to create an electrical contact over the areasadjacent to the grooves. The half-oval grooves allow the cooling tube 90to conform easily to the surface area of the grooves 43 and, thus,maintain thermal contact without impeding the electrical contact betweenmembers 41 or the flow of coolant within the cooling tube 90.

The shape or contour of channels 43 are subject to manufacturingvariances. If non-conformable tubes 90 were used therein and largevariances occurred in the dimensions and contour of the channels 43 orthe tubes, rigid cooling tubes 90 would not conform to the manufacturedshape of channel 43. This would create an air space produced between thetube 90 and groove 43. This problem is addressed in the backgroundpatents mentioned herein. These patents disclose the use of caulkingmaterial in the gaps to improve heat transfer. By using a conformablematerial for tube 90, such manufacturing variance problems would beautomatically overcome by the tendency of the tube 90 to conform to theactual contour of channels 43.

FIGS. 6(a) and 6(b), show a semi-circular groove 43 in member 41 and around coolant tube 90. If, after assembly of the cooling assembly 21,the coolant tube 90 fits perfectly within the surrounding grooves 43 inthe two plates 41, good surface-to-surface contact occurs between groove43 and the surface of tube 90. This condition is shown in FIG. 6(a).However, as shown in FIG. 6(b), if groove 43 is of different contourthan the natural shape of the coolant tube 90, or vise versa, the tube90 nevertheless conforms to the actual shape of groove 43 since it isconformable. Thus, intimate contact between the tube 90 and plate 41 isstill accomplished after the cooling assembly is assembled foroperation. The abnormalities in the surface or contour of groove 43shown in FIG. 6(b) are greatly exaggerated for the purposes of clarityof this description.

A preferred embodiment of the grooves 43 is shown in FIGS. 7a-b and8a-c. These figures which are enlarged schematic illustrations forclarity of description, are not to any scale and the components thereinare not necessarily proportionally sized with accuracy with regard toone another. In this embodiment, the groove 43, when a cross-sectionthereof is viewed, takes on the contour or profile of a truncated halfcircle in each plate. FIGS. 7a-b and 8a-c are partial cross sections ofthe cooling assembly similar to that shown in FIG. 5. When a conformablematerial is used for tube 90, a quasi-oval groove such as a truncatedhalf circle, rather than a half oval or half circle has been found to bea very advantageous shape for the grooves 90 in plates 41.

The term "truncated half circle" is described in conjunction with FIGS.7a and b. FIG. 7a depicts the cross section of a circle contour 50which, when used as is to form the grooves, produces a half circlegroove in each plate. The circle 50 has a horizontal center line 54dividing the circle into upper and lower halves. In order to form thetruncated half circle groove, a portion 52 of the circle 50 is cut awayas indicated by the cross hatched section of FIG. 7a. When this is done,the remaining portions of the upper and lower portions of the circle 50are bounded by upper half portion 56 and truncated edge 57 and lowerhalf portion 58 and truncated edge 59, respectively. Each of these formsa truncated half circle groove.

The plates 41 of the cooling assembly are assembled as shown in FIG. 7band the upper and lower truncated half circle grooves in each plate 41,when fitted together to provide a channel for the tube (not shown), forma truncated circle contour for the channel. A feature of the truncatedhalf circle grooves is that this shape provides room, at the edges 60 ofthe groove where the two plates 41 interface, for the walls of the tubeto expand. Both the oval and truncated circle channel profiles providemuch space which is used by the tube during the assembly and operationof the fuel cell. However, the use of the truncated circle profile inthe channel provides optimum contact between the tubes' outer surfaceand the surface of the groove while also providing room for expansion,especially during operation of the cell.

The interaction of the tube 90 with the truncated half circle grooves ineach plate is shown in FIGS. 8a-c. FIG. 8a shows the shape of grooves 43when plates 41 are assembled, but without the tube 90 within the channelprovided by grooves 43. The cross-section of the tube 90 is, however,superimposed in dotted lines, over the groove 43 to schematicallyillustrate that the natural shape of tube 90 is altered in thisembodiment of the invention when it is assembled with plates 41. FIG. 8bshows the tube 90 assembled with plates 41. The tube 90 takes theapproximate shape shown. The fuel cell has not been placed in operationas yet and, thus, the grooves 43 still leave some room for expansion inthe vicinity of edges 60.

FIG. 8c shows the grooves 41 and tube 90 when the fuel cell has beenplaced in operation and has heated up to its normal operatingtemperature. Coolant (not shown) is also flowing through the tube 90 inthis view. During the time that the fuel cell is brought up to operatingtemperature the materials therein expand. When Teflon is used for thecoolant tube 90, the Teflon expands faster and to a greater degree thanthe material of plates 41; e.g., a graphite plate. In addition, thecoolant flows through the tube 90 with a pressure which tends to pushagainst the interior wall of the tube 90 and expands its outer surfaceinto the vicinity of edges 60.

It can be appreciated, in contrast, that when the grooves 43 are formedby half circles and the channel for the tube 90 is in the shape of afull circle when the plates 43 are assembled, there is no room forexpansion of the tube 90. Thus, if the diameter of tube 90 isapproximately the same size as the groove, there is little place for thetube 90 to expand when the cell is brought up to operating temperatureand/or coolant is passed through the tube. Such expansion could forcethe plates 41 apart after assembly which would deteriorate the intendedperformance of the cell.

On the other hand, if the outer size of tube 90 was reduced relative tothe groove size to allow adequate expansion room within the groove, thesmaller tube would be able to flop around in the plates after assemblywhenever the cell is not at full operating temperature. This isdisadvantageous in that it may cause damage to the coolant tube, such asduring shipping and handling of the fuel cell, and little of the tube'speriphery would be continuously in place against the surface of grooves43 at all times.

The sizes of the grooves 43 and outer diameter of tube 90 are to bechosen so that as much of the periphery of the tube as practical is incontact with the surface of the groove during operation of the cell.However, these sizes, necessarily, should not be such that the expansionof the tube due to the bringing of the cell to operating temperature andthe passing coolant through the tube makes the tube force the plates 41apart. In sizing these elements, it is preferable to leave a slight airgap between the groove edges 60 and the periphery of the tube 90 thanrisk separation of the plates. A small air gap, such as that shown inFIG. 8c, does not appreciably cut down on the passage of heat from theplates 43 to the coolant in the tube 90. It does, however, provide areasonable manufacturing tolerance for the grooves and tube.

The actual size of the tube and the profile of the groove are intimatelyrelated to provide the desired surface contact between the two elements.These factors are dependant on the application also. The selection ofthe size of the tube depends, among other things, on the amount ofcoolant required and the thickness of the tube wall. Once these factorsare decided upon and the peripheral size of the tube to be used isdetermined, the size of the periphery of the tube at cell operatingtemperature and with coolant therein can be determined. This, in turn,is taken into account along with the plate material used to determinethe size of the groove to provide optimum contact between the groove andtube. The optimum system results when the tube has substantial contactwith the groove when the cell is not at operating temperature, as shownin FIG. 8b, and almost, but not complete contact with the groove whenthe cell is at operating temperature, as shown in FIG. 8c. In thismanner, certain areas of the tube's surface are always in contact withthe surface of the groove thereby eliminating the possibility of newgaps being generated between the two as the fuel cell is cycled on andoff or over a range of operating temperatures.

In the cooling assembly embodiment shown in FIG. 5, a polymeric coolingtube 90 is nestled between two grooved members 41 bonded to one anotheralong two narrow strips adjacent to the edges parallel to the straightsections of the cooling tube. Cooling plate materials suitable for hightemperature operation and corrosive environment would include strips ofpolyethersulfone film sandwiched between and bonded to two groovedmembers 41 made of graphitized or carbonized plates. An alternativeembodiment is possible which holds the same grooved members 41 togethermechanically until after they are assembled into a fuel cell stack ofother device in need of cooling. Still another alternative assemblytechnique is to hold the plates together with the tube in the channelwith a bonding medium such as dissolved polyethersulfone which is curedto an appropriate temperature.

The nature of the member 41 need not be constrained unduly. The shape ofgroove 43 could be constructed so as to deliberately conform the tube 90into intimate surface contact with groove 43; for instance, an elongatedor oval cross-section rather than circular. Also extremely hardmaterials need not be used for member 41. The materials used for member41 in this configuration could be materials which in of themselvesconform or collapse around the tube 90 so that intimate contact is fullyreached with the tube. The cooling tube can be pressed into half-ovalshape grooves cut out of whatever surface or surfaces are to be cooled.In this case, the cooling assembly 21 could consist merely of a Teflontube and cooling fluid. The complete absence of metal would give thisassembly corrosion resistance superior to that of metallic or partlymetallic devices whether coated or not.

The cooling tubes themselves or the entire cooling assembly, can be madeof a non-corroding material for use in a fuel cell stack. The primaryadvantages of this constriction are an easy and low cost fabrication,total safety against corrosion (non-metallic) and total elimination ofshunt currents between cooling plates in the stack without having tootherwise electrically isolate the cooling plates. The flexibility ofthe cooling tube also provides good thermal conduction thereto in ofitself since it tends to be pressed up tightly against the surfaces ofthe grooves in the members 41. The tube assembly is temperaturetolerant, totally corrosion resistant and totally impervious.

It is to understood that the above described embodiment of the inventionis illustrative only, and that modifications thereof may occur to thoseskilled in the art. Accordingly, this invention is not to be regarded aslimited to the embodiment as disclosed herein, but is to be limited onlyas defined by the appended claims.

What is claimed is:
 1. A cooling assembly for use in removing heat froma fuel cell having means for circulating coolant through the coolingassembly adjacent the cell, the cooling assembly comprising:(a) abendable length of flexible conformable material having the capabilityof withstanding the corrosive materials of a fuel cell environmenthaving a coolant passageway along the length thereof said passagewayhaving a plurality of straight parallel sections spaced one from anotherand also having a plurality of bend sections coupling said parallelsections in serpentine configuration and (b) means located within thepassageway formed as coils within the bend sections for enhancing theability of the flexible material to bend into relatively small radiiwithout crimping, said last mentioned means being formed straight withinthe straight parallel sections with the passageway maintaining itsability to carry coolant along the length of the material, of the coil.2. The assembly of claim 1 wherein the conduit means is metal-free. 3.The assembly of claim 1 wherein the conduit means ispolytetrafluoroethylene and the coil means is a metallic material. 4.The assembly as set forth in claim 1 and further including means forholding the conduit means in the cooling assembly including at least onemember which, when assembled with the conduit means, conforms at least aportion of the conduit means into intimate contact with the member. 5.The assembly as set forth in claim 4 wherein the means for holding theconduit means comprises at least one plate supporting said conduitmeans, the plate provided with grooves for conforming at least a portionof the conduit means into intimate contact with the plate.